* Oleg Nesterov | 2012-09-03 17:26:09 [+0200]: >Afaics the usage of update_debugctlmsr() and TIF_BLOCKSTEP in >step.c was always very wrong. > >1. update_debugctlmsr() was simply unneeded. The child sleeps > TASK_TRACED, __switch_to_xtra(next_p => child) should notice > TIF_BLOCKSTEP and set/clear DEBUGCTLMSR_BTF after resume if > needed. > >2. It is wrong. The state of DEBUGCTLMSR_BTF bit in CPU register > should always match the state of current's TIF_BLOCKSTEP bit. > >3. Even get_debugctlmsr() + update_debugctlmsr() itself does not > look right. Irq can change other bits in MSR_IA32_DEBUGCTLMSR > register or the caller can be preempted in between.
ptrace and uprobe are calling this function from process context. As long as you have here get_cpu() instead of local_irq_disable() you should be safe here. The only user that is touching this bits in irq context is perf. perf uses raw_local_irqsave() (raw_* most likely due to -RT). I have no idea what you can against NMI unless not touching the register in NMI context. Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
